text: The LIFT system measures chlorophyll fluorescence by stimulating the plant with excitation light, leading to an increase in fluorescence to its maximum (Fm). The naturally occurring fluorescence (F) can also be measured without the excitation light. The variable fluorescence (Fq) can be calculated as the difference between Fm and F'. The Photosystem II operating efficiency can be calculated using the equation:
  For the relaxation sequence (RQA), different relaxation parameters can be calculated according to different time sections:
  * F, ~ 0.625 ms after the maximum Fluorescence has occurred and
  * F, ~ 6.5 ms after the maximum Fluorescence has occurred.
  These parameters can be used for calculating the reoxidation efficiency of Q i.e. the kinetics of electron transfer between QA to PQ pool to photosystem I for light-adapted plants.